This invention relates to a process for refining edible oil to retain maximum antioxidative potency, the resultant refined edible oil and mixtures of that oil with other edible oils.
Fats and oils (oils are just liquid fats) are stable food products, because they contain virtually no water, and, thus, microorganisms cannot thrive or grow in them. However, they do react with water and/or oxygen and under influence of light, trace metal ions such as iron, copper and other metal ions, resulting in off-odors and bad flavor, known as rancidity. The rapidity of the onset of rancidity is much greater at high temperature (as the ones used in preparation of food). Each oil has its own stability, which varies with two factors:
a) One factor is the ratio in the oil of saturated fatty acids to unsaturated fatty acids. There are two types of unsaturated fatty acids: monounsaturated and polyunsaturated. The saturated fatty acids are the least vulnerable and the polyunsaturated the most vulnerable to degradation. PA1 b) The other factor is the content and effectiveness of antioxidants and antioxidant precursors naturally occurring in the oil. Antioxidants are compounds that react with free radicals and inhibit free radical chain reaction. Oil seeds or other raw material for oil may, apart from actual antioxidants, contain compounds that are not per se antioxidants (which do not interfere with free radical formation) but the chemical structure of which may under certain circumstances change into actual antioxidants. These compounds are called "antioxidant precursors". PA1 1. Degumming PA1 2. Neutralization PA1 3. Bleaching PA1 4. Deodorization PA1 1. Degumming is generally carried out using 1%-3% by weight water or aqueous solution of phosphoric acid based on the weight of the oil, and heating at 60.degree. C.-85.degree. C. for 10 to 30 minutes. The process removes the bulk of phospholipids or "gums" and proteinaceous matter and reduces color components and trace metals. PA1 2. The neutralization involves the addition of dilute alkali to remove free fatty acids from the oil. The acids are converted to soaps, which are removed by centrifugation, decantation or running off the soap stock from the bottom of the vessel. Neutralization conditions vary: contact time 2 to 15 minutes and temperature 70.degree. C. to 95.degree. C., depending on batch or continuous process. The oil is then subjected to hot water washings to remove most of the soaps and the oil is then dried under vacuum. PA1 3. The primary object of bleaching of the neutral oil is to remove major portions of colored substances present. Traditionally, alkaline or acid natural clays have been used; recently, acid-activated clays are most common. All the aforementioned clays, known generically as "bleaching earth," tend to efficiently absorb color components. Bleaching earth not only removes color pigments but also trace metals and any residual soaps remaining from the neutralization process. The removing of trace metals is important as such components act as catalysts for free radicals. Normal bleaching conditions can be 0.5 to 2% by weight activated bleaching earth, based on the weight of the oil, the temperature 90.degree. to 110.degree. C., contact time 15 to 30 minutes and pressure 20-50 mbar. Thermal bleaching, i.e., bleaching without the aid of bleaching earth, conditions can be 240-260.degree. C., the time 45 to 120 minutes and pressure 1-6 mbar. PA1 4. Deodorization, the last refining stage, is employed to remove off-flavor components, including residual free fatty acids, mono- and diglycerides and any color decomposition products. Deodorization conditions are: temperature 210-270.degree. C. and holding time 3-8 hours for batch process and 15 to 120 minutes for continuous and/or semi-continuous deodorization. The steam consumption is 5 to 10% by weight, based on the weight of the oil, in batch, and 1 to 3% by weight, based on the weight of the oil, in continuous/semi-continuous deodorization. The pressure is 1-6 mbar. The traditional refining steps not only remove undesired compounds; they also remove or considerably reduce the content of a large number of desired components such as natural antioxidants, antioxidant precursors, polymerization inhibitors and vitamins. Part of the desired components may still be present before the last conventional refining step, deodorization, but then decrease substantially or disappear due to the high temperatures used in the deodorization process.
It is common to add synthetic antioxidants such as butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), propyl gallate and tertiary butyl hydroxy quinone (TBHQ) to oils. They are mainly used to inhibit oxidation during the storage of oil. They are too unstable to have any useful function if the oil is used for frying. Also, there is among the public a growing concern that synthetic chemicals may not be safe and synthetic material in food is often mentioned in connection with allergic reactions.
It is an object of the invention to provide a process for refining crude edible oil so that an unusually high degree of naturally occurring antioxidative power is retained in the refined oil.
It is a further object of the invention to provide a refined edible oil having an unusually high degree of naturally occurring antioxidative power.
It is a yet further object of the present invention to provide a refined edible oil selected from the group consisting of sesame seed oil, rice bran oil, wheat germ oil, oat germ oil, coffee oil, tea seed oil, pine seed oil and mixtures of any of the foregoing containing at least about 50%, by weight, preferably at least about 60%, by weight, and most preferably, at least about 75%, by weight, of the antioxidants and antioxidant precursors naturally occurring in the crude edible oil, considered cumulatively.
Other objects and advantages of the invention will be apparent from the following description of the invention.